1. Field of the Invention
The present invention pertains generally to the cutting of glass by means of an abrasive fluid jet and more particularly to the cutting of glass along any desired line of cut, including intricate patterns, at relatively high speed with resultant high quality cut surfaces by means of an abrasive fluid jet directed against the glass.
2. Description of the Prior Art
Because of its extreme hardness and frangible nature, unique problems are presented in the cutting or severing of glass. Conventional glass cutting actually involves a controlled breaking or fracturing of the glass. Thus, the surface of the glass is scored by a relatively harder instrument along the desired path of fracture, and the glass is then flexed along the score line to cause it to fracture and separate along this line. While such a procedure is satisfactory for certain purposes, it also has many limitations. A glass sheet is very rigid and it must be flexed along the score line to cause the final fracture. As will be apparent, while the sheet can be readily flexed along a straight score line, extending substantially across the sheet, flexing is much more difficult along score lines of an interior cutout and becomes nearly impossible for such openings of small dimensions. Flexing along a curved score line may be troublesome, and it becomes increasingly difficult as the degree of curvature increases. Flexing along lines with short radii of curvature is virtually impossible so that intricate patterns can be cut only with great difficulty, if at all. Likewise, formation of small mounting openings as commonly required in present day automobile sidelites is not feasible by this method, so that such openings must generally be formed by means of a diamond drill.
The procedure is effective in cutting relatively thin glass wherein, because of the depth of the score mark relative to the total glass thickness, the fracture will follow the score line. However, in cutting thicker glass by this method the line of fracture may not follow the score line so that a ragged edge is formed, or the glass may actually fracture along a random line, destroying the glass sheet. The difficulty of cutting increases as the thickness increases, so that cutting very heavy glass is time consuming and expensive, and the yield of useable glass is relatively low. The method also tends to leave a sharp edge at the surface opposite the score line, which is objectionable in additional fabricating steps.
Other systems such as so-called hot line cutting, wherein the glass is heated along a line and then chilled to cause fracturing along the line, and cutting with a diamond saw, have been suggested for cutting glass and particularly thick glass. However neither has proven entirely satisfactory in a commercial operation, and particularly for production of other than straight line cuts. Such methods tend to be slow and expensive and may create undesirable stresses in the glass. They also are not readily adapted to cutting complex shapes in glass.
The concept of liquid jet cutting of various materials is known in the prior art, as is the use of abrasive particles in conjunction with the liquid jet. While it is suggested, for example, by U.S. Pat. No. 3,888,054, that hard or brittle materials such as glass may be cut by a stream of abrasive particles carried in a fluid, it is also disclosed that the workpiece should be immersed in a liquid to avoid abrading away of the surface adjacent the cut. U.S. Pat. No. 4,380,138 discloses abrasive liquid jet cutting wherein abrasive particles are positioned adjacent the surface of the material to be cut and then driven into the workpiece by the liquid jet, and suggests that it was previously unknown to add abrasive particles directly to high velocity liquid cutting jets. In any event, the prior art is not believed to appreciate the cutting of glass with an abrasive fluid jet in the manner and at the pressure contemplated by the present invention.
Thus, it has been found that when flat glass sheets of thicknesses in general commercial use are initially impacted interiorly of their periphery by an abrasive fluid jet pressurized to a level materially exceeding 10,000 psi, as in forming holes or interior cut-outs in the glass, chipping, severe venting or shattering of the glass at the point of impact is likely to occur. The vents and chipped edges may extend into the adjacent glass part, rendering it unuseable for its intended purpose. Consequently, it has heretofore generally been considered necessary for such cutting on a large scale to be done with a fluid under a pressure on the order of 10,000 psi or less in order to prevent damage to or destruction of the glass. The line or cutting speed is a function of the degree of pressurization of the abrasive fluid, and at this pressure the cutting speed is so limited as to make the procedure marginally useful for commercial purposes.